1. Field of the Invention
This invention relates to a process for preparing polyolefins using a novel polymerization catalyst. More particularly, it is concerned with a process for preparing polyolefins by polymerizing or copolymerizing olefins in the presence of a catalyst consisting of a solid component and an organoaluminum compound and/or an organozinc compound, said solid component being obtained by copulverizing (1) a magnesium halide and/or a manganese halide, (2) an aluminum oxyhalide and (3) a titanium compound and/or a vanadium compound, whereby the yield of polymer per solid and that per transition metal are increased to a remarkable extent resulting in the step of removing residual catalyst in the polymer becoming unnecessary and the molecular weight distribution of the polymer is expanded resulting in the fluidity of the molten polymer beig improved.
2. Description of the Prior Art
In the technical field of this sort, there have heretofore been known many catalysts consisting of, as carrier, an inorganic magnesium solid such as magnesium halide, magnesium oxide and magnesium hydroxide, and a compound of transition metal such as titanium and vanadium supported thereon (see, for example, Japanese Patent Publications Nos. 13050/68 and 9548/70). However, polyolefins prepared by use of such carriers have a relatively narrow distribution of molecular weight; in practical use, they are in some cases preferred in the field of injection molding, but in the field of extrusion molding and blow molding their use results in poor surface condition of the resulting molded article such as the occurrence of shark skin on the surface and thus there is a significant drawback in their practical use. Of course, even with the above-mentioned carriers, it is possible to expand the molecular weight distribution to some extent by the selection of polymerization temperature and cocatalyst, but it has heretofore been impossible to expand the molecular weight distribution to a substantially satisfactory extent.
Ziegler catalysts containing an aluminum oxyhalide as one component are known from Japanese Patent Publication No. 2712/69. Howeger, the activity of such catalyst is not sufficient, far from dispensing with step of removing residual catalyst, and the molecular weight distribution of the resulting polymer is not fully wide and an improvement in fluidity has been desired.
Polyolefins having a wide molecular weight distribution are characterized by having a large flow parameter which is defined by the expression given below. Also in the present invention, this flow parameter will be referred to hereinafter as being indicative of the extent of the molecular weight distribution. ##EQU1##